The isomerization of normal paraffins of low molecular weight is highly important in the oil industry in view of the very high octane number of the isoparaffins formed.
Modifications in the regulations in force in the main industrialized countries, concerning the quality standards for motor-car gasolines and the progressive elimination of lead-containing additives, oblige the producers of said products to search for improved processes for obtaining lead-free motor-car gasolines of high octane number. The processes for converting normal paraffins having for example 4, 5, 6, or 7 carbon atoms per molecule, particularly n-paraffins of 5 and 6 carbon atoms per molecule, to a product of high isoparaffin content are of particular interest.
By these processes, in particular, the octane number of the light gasoline fractions, such as straight-run gasolines or for example those obtained by catalytic reforming, are improved. The mechanism of the hydroisomerization reaction is usually considered to be a bifunctional mechanism for which the preferred catalysts are those comprising simultaneously acid sites and sites having a hydrogenating/dehydrogenating function.
In the last twenty years, many papers mention the use, in hydroisomerizatin processes, of catalysts essentially formed of zeolites more or less deeply modified, particularly mordenites, usually in acid form, with a hydrogenation promoter. As an example, patents to SHELL Company concern the use of catalysts essentially formed of mordenites modified according to particular processes : U.S. Pat. Nos. 3,842,114, 4,359,409 and 4,400,576.
Other relevant patents are patents to ESSO Company using partially dealuminated mordenites : U.S. Pat. Nos. 3,480,539 and 3,506,400, and a patent of MOBIL Company, U.S. Pat. No. 3,551,353.